What the Invoice Due-Date Calculator does
This calculator works out when an invoice is actually due. It handles net terms, end-of-month terms, a fixed day of the following month, prox terms with a cut-off, and terms running from delivery rather than from the invoice date - then rolls the result off weekends and the public holidays you list, in whichever direction your contract specifies.
It also prices an early-payment discount. "2/10 net 30" is not a small courtesy: refusing it costs about 37% a year in simple terms, which is more expensive than almost any overdraft. The page shows both the simple and the compounded figure, because the two differ considerably and finance textbooks quote the first while the arithmetic favours the second.
How to use it
- Enter the invoice date and choose the payment term. Net terms count days from the invoice; EOM terms count from the end of the invoice month; prox terms land on a fixed day of a later month depending on a cut-off.
- Set what happens when the date falls on a non-working day, choose the weekend pattern and list any public holidays.
- Add the early-payment discount if there is one - the percentage and the number of days it must be paid within.
- Read the due date, the days remaining or overdue, and the annualised cost of not taking the discount.
- Download an .ics reminder for the discount deadline and the due date, or copy the summary into the invoice record.
Reading the results
The contractual date is what the terms produce before any rolling. The due date is where it lands after weekends and holidays. Both are shown, because a dispute about lateness is usually a dispute about which of the two applies.
The credit period is the number of calendar days from the invoice date to the rolled due date - the figure that actually matters for working capital, and often longer than the headline "30".
"Cost of not taking the discount" is an annual rate. Compare it with what your own money costs: if you can borrow at less than that rate, taking the discount is free money.
Days overdue count from the due date to the date in the "treat today as" box, so you can price a claim as at any date.
Worked example: net 30 with 2/10, invoiced 15 January 2026
Fifteen January 2026 is a Thursday. Net 30 gives a contractual due date of 14 February, which is a Saturday, so rolling forward makes it Monday 16 February - a credit period of 32 days rather than 30.
The discount is 2% if paid within 10 days, so the deadline is 25 January. Paying then rather than on day 30 means finding the money 20 days early in exchange for 2% off.
The cost of that money is 2/98 = 2.0408% for 20 days. Annualised simply, 2.0408% x 365/20 = 37.24% a year. Compounded over the 18.25 twenty-day periods in a year it is 44.58%. Either way, an organisation that can borrow at 8% and lets a 2/10 discount lapse is losing money on purpose.
On a 4,800 invoice the discount is 96.00, so 4,704.00 settles it by 25 January against 4,800.00 on 16 February.
Formulas and scoring rules
- Net terms
due = invoice date + N days- End of month plus N
due = last day of the invoice month + N days- Nth of the following month
due = day N of the next month, clamped to the last day if N does not exist- Prox with a cut-off
due = day N of the next month, or the month after when the invoice day is past the cut-off- Cost of refusing a discount, simple
rate = d/(100 - d) x 365 / (net days - discount days)d is the discount percentage. 2/10 net 30 gives 37.24% a year.- Cost of refusing a discount, compounded
rate = (1 + d/(100 - d)) ^ (365 / (net days - discount days)) - 144.58% for 2/10 net 30 - the same cash flows, compounded rather than multiplied.
The terms that mean different things to different people
"Net 30" usually means thirty days from the invoice date, but some trades count from the statement date, some from delivery and some from receipt of a valid invoice - which can be weeks later if the invoice was rejected. "EOM" can mean the end of the invoice month or thirty days after it. "10th prox" means the tenth of the following month, but only if the invoice arrived before the cut-off.
None of these is defined by a standard, so the calculator offers each one explicitly rather than trying to parse a phrase. Work out the date your reading of the contract produces, then check the wording - particularly the trigger, which is where most late-payment arguments actually start.
Rolling, and which direction
Rolling forward to the next working day is the common commercial convention and the one most payment runs use in practice. Rolling backward is used where the terms are a hard limit, and some contracts simply say nothing, in which case the raw date stands and a Saturday due date means a Friday payment run.
The choice matters at month ends: a 31 January due date rolled forward lands in February, which can move the payment into a different accounting period for both parties.
Limitations: what the result does not prove
- It applies the term you select. It does not read your contract, and the wording of the contract always wins.
- It knows only the public holidays you type in. There is no holiday calendar, no region setting and no assumption about which country you are in.
- It does not calculate late-payment interest or statutory compensation. Entitlement, rates and the reference rate to use are matters of local law.
- The discount economics assume the invoice would otherwise be paid exactly on the due date. If you habitually pay late, the real comparison is against your actual payment date, not the terms.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- ISO 8601-1 - Date and time: basic rules - checked 19 Sep 2026
- RFC 5545 - Internet Calendaring and Scheduling Core Object Specification - checked 19 Sep 2026
Frequently asked questions
What does net 30 mean?
Payment is due thirty days after the invoice date, with the full amount payable - "net" meaning no discount applies. What differs between contracts is the trigger: some count from the invoice date, some from delivery, and some from receipt of a valid, undisputed invoice.
What does 2/10 net 30 cost if I do not take it?
About 37% a year in simple terms, or 44.6% compounded. Refusing a 2% discount to keep the money 20 extra days is borrowing at 2/98 for those 20 days, which annualises far above any ordinary credit line. The page shows both figures for whatever discount you enter.
What is the difference between EOM and prox terms?
EOM terms count from the last day of the invoice month - "EOM plus 30" from a January invoice is due 2 March. Prox terms land on a fixed day of a later month: "10th prox" is the tenth of the following month, pushed a further month when the invoice is dated after the cut-off day.
What happens if the due date falls on a weekend or holiday?
It depends on the contract. Rolling forward to the next working day is the usual commercial convention; some terms roll backward so the limit is not exceeded, and some say nothing. The calculator shows the contractual date and the rolled date separately so you can see which one you are relying on.
Does a due date on the 31st work in February?
Yes - it is clamped to the last day of the month. A term of "the 31st of the following month" from a January invoice lands on 28 February in a common year and 29 February in a leap year, which is what commercial practice does with an impossible date.
Can I charge interest on a late invoice?
Often, but the right, the rate and any fixed recovery costs are set by local law or by the contract, and both vary widely. This page tells you how many days late the invoice is; what that entitles you to is a legal question.
Is the invoice data sent anywhere?
No. Dates, amounts and holiday lists stay in the browser. The .ics reminder is generated locally and downloaded straight to your device.
Last reviewed by the A2Z.Tools team against the sources listed above.
